Leicester City's hopes of retaining the FA Cup came to a brutal end in a 4-1 drubbing away to Midlands rivals Nottingham Forest in the fourth round at a rocking City Ground on Sunday.
In the first clash between the clubs for eight years, a rampant Forest scored three times in 10 manic first-half minutes with Philip Zinckernagel, Brennan Johnson and Joe Worrall all punishing some flimsy Leicester defending.
Second-tier Forest's buoyant fans were briefly silenced when Leicester grabbed a lifeline before halftime as Kelechi Iheanacho pounced on an error to score from an acute angle.
But there was no stopping the hosts and they continued to dominate their supposed superiors after the break and restored their three-goal margin when Djed Spence slotted home.
Forest have now beaten Arsenal, the FA Cup's most successful club, and the holders in consecutive rounds and will be eyeing a quarter-final place after being drawn to play Championship rivals Huddersfield Town in round five.
To compound Leicester's misery a fan from the away section ran on to the pitch as Forest's players celebrated their third goal, landing punches before being dragged away.
That ugliness aside it was a memorable day for Forest, and the competition, as a sell-out crowd roared them to a deserved win against a Leicester side who surrendered all too meekly.
"The first words are for the supporters," Leicester manager Brendan Rodgers said.
"You come into a derby game and looking to win the FA Cup again, the supporters will have expected to see the team play with authority, aggression and a strong mentality. We apologise for that, that was nowhere near the level."
For Forest it continued a remarkable transformation since Steve Cooper replaced Chris Hughton as manager in late September with the former European champions bottom of the Championship.
They have risen to eighth in the table and against Leicester they looked like a team brimming with confidence.
"The lads kept going, scored four, hit the bar and could have got one or two others. We were excellent and really pleased for the boys and proud of the club," Cooper said.
Forest served notice of their intent in an evenly-balanced opening when Keinan Davis rattled the frame of the Leicester goal with a great effort.
Cooper's side went ahead in the 23rd minute when the outstanding Johnson crossed to the far post, Davis headed back across goal and Zinckernagel reacted quicker than any Leicester defenders to bundle home.
Forest's fans were still celebrating that when Leicester's defence imploded again a minute later. This time a dreadful back pass by James Justin was intercepted by Johnson and he coolly slotted the ball past keeper Danny Ward.
When an unmarked Worrell met a corner and his header bounced beyond Ward to make it 3-0 in the 32nd minute the home supporters were in dreamland and it was all too much for one Leicester fan whose actions could have serious repercussions.
Forest keeper Brice Samba's ill-advised decision to try and intercept a ball played forward left him stranded and he was punished by Iheanacho's cool finish into an empty goal.
Leicester's hopes of a second-half comeback never really looked realistic though and when Zinckernagel and Spence combined for the latter to fire home just past the hour mark the game was up for Rodgers's side.
"It is a really poor performance, it is about hunger in the team," Rodgers, whose side face Liverpool in the Premier League next, said. "This team have been together for three years and I see some worrying signs with some of the players."
Leicester condemn fan for attacking Forest players
Leicester City said they are appalled after one of the club's supporters ran on to the pitch and attacked Nottingham Forest players during their heavy FA Cup defeat on Sunday.
The Cup holders went down 4-1 to their Midlands rivals and later issued a statement to condemn the fan who charged on after Forest's third goal and appeared to land punches before being bundled away.
"The club is appalled by such behaviour and offers its apologies to Nottingham Forest and its players whose safety was compromised," Leicester said in a statement.
"We applaud the swift action taken by City Ground stewards in apprehending the individual involved, who will be subject to a lifetime ban from all Leicester City fixtures at home and away. We will offer every support to the relevant authorities in pursuing further appropriate action."
Nottinghamshire Police later confirmed that a man had been arrested in connection with the incident.
"Investigations are in the very early stages and our enquiries into the circumstances surrounding the incident are ongoing," a statement read.
It was the first meeting between the rivals for eight years and 4,000 Leicester fans made the short trip for the eagerly-awaited tie at a sold-out City Ground.
Asked about the incident, Leicester manager Brendan Rodgers said: "It's behaviour we do not want to see. The field has to be a safe environment, we must always retain the respect in football and unfortunately the guy has come onto the pitch.
"The rules of society have changed -- there's no respect. People feel entitled to think they can do these things. We can't have that lack of respect."
Former Leicester striker and now BBC Sport presenter Gary Lineker described the fan as a "disgrace".
"Whoever that so called fan was who ran on to the pitch throwing punches at @NFFC's players should be banned for life by
@LCFC. An embarrassment and a disgrace," he said on Twitter.